Abstract
BackgroundThe calcitic brachipod shells contain proteins that play pivotal roles in shell formation and are important in understanding the evolution of biomineralization. Here, we performed a large-scale exploration of shell matrix proteins in the brachiopod Laqueus rubellus.ResultsA total of 40 proteins from the shell were identified. Apart from five proteins, i.e., ICP-1, MSP130, a cysteine protease, a superoxide dismutase, and actin, all other proteins identified had no homologues in public databases. Among these unknown proteins, one shell matrix protein was identified with a domain architecture that includes a NAD(P) binding domain, an ABC-type transport system, a transmembrane region, and an aspartic acid rich region, which has not been detected in other biominerals. We also identified pectin lyase-like, trypsin inhibitor, and saposin B functional domains in the amino acid sequences of the shell matrix proteins. The repertoire of brachiopod shell matrix proteins also contains two basic amino acid-rich proteins and proteins that have a variety of repeat sequences.ConclusionsOur study suggests an independent origin and unique mechanisms for brachiopod shell formation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12953-015-0077-2) contains supplementary material, which is available to authorized users.
Highlights
The calcitic brachipod shells contain proteins that play pivotal roles in shell formation and are important in understanding the evolution of biomineralization
SDS-PAGE of the soluble organic matrix extracted from the secondary layer showed two major bands (< 6.5 and 12 kDa) and a minor band of 62 kDa when stained with Coomassie Brilliant Blue (CBB) (Fig. 1a)
Silver staining showed a major band at 35 kDa and many minor bands in addition to the three bands stained with CBB (Fig. 1b)
Summary
The calcitic brachipod shells contain proteins that play pivotal roles in shell formation and are important in understanding the evolution of biomineralization. We performed a large-scale exploration of shell matrix proteins in the brachiopod Laqueus rubellus. Many organisms have a diversity of biominerals that have a large number of ecologically important functions, including body support and defense against predators. Most metazoan biominerals are likely acquired independently in different phyla in the early Cambrian [1]. A crucial factor in understanding the mechanisms and evolution of biomineralization is an in-depth analysis of the organic matrix present in hard tissues. A large number of skeletal proteins have been identified and their roles in the biomineralization process have been analyzed [3]. Brachiopods are marine invertebrates that appeared in the Cambrian and have two valves composed of calcium carbonate or calcium phosphate
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